It has long been realised that particular fossils tend to occur together in assemblages. In the past 25 years these assemblages have attracted a good deal of interest with the development of a branch of palaeontology called palaeoecology, in which attempts are made to identify and describe original communities of animals. Several examples of trilobite assemblages have been described from Wales in recent years. In the lower Ordovician rocks of the Carmarthen area, Dyfed, Dr. R.A. Fortey of the...

Fully grown trilobites range in size from a millimetre to over 50 centimetres, though on average they are in the range of 3 to 4 centimetres long. The rocks of Wales have yielded examples from both extremes of the size range, from the tiny Shumardia from lower Ordovician rocks near Arennig Fawr, Gwynedd, to Salter's giant Paradoxldes. The morphology of many trilobites diverges considerably from the popular conception of these fossils, and those which have been found in Wales include a wide...

Clarkson and Levi-Setti made experimental models, and the slight differences in the refractive indices between the upper and lower part of the lens operate with the wavy correcting surface to produce a sharp, anastigmatic focus. Trilobites with such sophisticated eyes may have been nocturnal, or perhaps lived in conditions of low illumination. A great variety of eyes are known and certain groups of trilobites developed enormous eyes. In Pricyclopyge they occupied...

A most distinctive feature of many trilobites is the pair of prominent eyes on the headshield. When examined with a lens, the trilobite eye can be seen to be compound - made up of a large number of individual facets, reminiscent of the eye in some living arthropods. Trilobite eyes are of special interest on two counts, firstly that they are the most ancient visual system known, secondly in their high degree of sophistication. It has long been recognised that there are two major types....

'A good collection of well-arranged trilobites looks better in the cabinet than perhaps any other fossils', wrote J.E. Taylor in Our Common British Fossils, published in 1885. Such is their popular appeal that trilobites have always been some of the most eagerly sought after of all fossils. Their name, suggested by their singular three-lobed appearance is derived from 'Trilobitae', introduced by the German naturalist Johann Walch in 1771 in his Der Naturgeschichte der Versteinerungen 'Natural...

The geological history of trilobites spans some 350 million years. They appeared suddenly early in the Cambrian Period, and some of the oldest Cambrian rocks in many parts of the world contain abundant trilobites. This is not the case, however, in Wales where these rocks have so far yielded very few fossils, even though it is the historical type area for the Cambrian System. This is due in part to the fact that many of these rocks have been strongly deformed, obliterating all traces of fossils...